Wes Rolley on sat 4 jan 03
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At 10:41 PM 1/3/03 -0500, Elizabeth wrote:
>On most of their glazes, I'm
>setting my top temp in my ramp mode 30=B0 lower than their schedule with
>the rest of the schedule identical....watching my cones very carefully
>and getting cone 6. It takes time and patience and lots of testing to
>work it out. My kiln overfires at their temperature. I have come to the
>conclusion that because my kiln can't keep up with the speed of the
>ramp, I'm getting more heat work before it gets anywhere near the top
>temp.
This is probably true. I single fire in a Skutt 1027. I also like to slow=
=20
cool my glazes, especially those with substantial amounts of magnesia=20
(dolomite). After a lot of mistakes, which I will euphemistically call=20
"testing", I ended up with the following schedule, which probably does not=
=20
work for anyone else but myself, using my preferred clay body (Cinnamon=20
from Claymaker, San Jose, CA).
R/H Segment Rate Temp.F Hold
1 150 200 0-? depending on thickness / dryness of=
ware.
2 150 900 0
3. 100 1100 0
4 135* 2100 0
5 108 22??** 15
6 9999 1960 0
7 150 1550 0
* This is slow, but I found that I had less problems with off gassing,=20
black core, etc. Like a slow bisque.
** The high temperature depends on the desired cone. For example, 2220 F=20
gives me a cone 8 almost touching. In a recent firing with some high mass=
=20
pieces, 2272 gave a slight over fire at cone 10 (cone flat, glaze went=20
transparent in spots with higher gloss than desired).
A firing normally requires around 22 hrs. from start to shut off at=20
1550. I can get a 48 hr. turn around on loads. Start a firing around noon,=
=20
close the lid around 8:30, reach maximum temperature between 4:00 and 6:00=
=20
AM, unload the next morning.
Which leads me to the conclusion that the best practice is to check the=20
cones visually as the kiln near top temperature and then, if necessary, to=
=20
reprogram the temperature for segment 5 so that I either extend the firing=
=20
or cut it off short. I wish that there were a more automatic method, just=
=20
because I am lazy and do not want to get up at 4 or 5:00 AM to check the=
kiln.
I have also found that the total mass inside the kiln will make a=20
measurable difference in the temperature reading at which I reach a given=20
cone...normally 8-10.
"I find I have a great lot to learn =96 or unlearn. I seem to know far too=
=20
much and this knowledge obscures the really significant facts, but I am=20
getting on." -- Charles Rennie Mackintosh
Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037
wrolley@charter.net
(408)778-3024
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